In refrigerant handling systems, such as refrigerant recovery and/or recycling systems using a compressor, it is conventional to separate lubricant (oil) while transferring the refrigerant. (The term "lubricant" is employed in the broad sense to include both natural and synthetic "oils" and other types of refrigeration system lubricants.) In U.S. Pat. No. 4,768,347 for example, the recovery compressor has its own lubricant sump, and the main or system lubricant separator is located upstream of the compressor inlet in an effort to minimize mixing of the lubricant in the refrigerant being recovered with the compressor lubricant. For service of automotive air conditioning systems and other small refrigeration systems, a lubricant separator such as that disclosed in U.S. Pat. No. 4,809,520 is large enough to hold the entire charge of lubricant collected from the system under service. The collected lubricant is drained through a valve and measured after each recovery operation, so that the same amount of lubricant can be replaced when recharging the refrigeration system under service.
In refrigerant handling systems employing oiled compressors, it is also conventional to provide a separator for recovering and recycling the compressor oil, as disclosed in U.S. Pat. No. 5,042,271. In such systems, there is thus typically a system lubricant separator upstream of the compressor inlet and a compressor lubricant separator downstream of the compressor outlet. It has also been proposed to employ oil-less compressors having no internal oil sump. Some oil-less compressors cannot operate for long periods of time downstream from a very high quality lubricant separator. In such situations, as noted in Manz, The Challenge of Recycling, Business News Publishing, 1995, page 22, a single lubricant separator with drain is disposed downstream of the compressor outlet.
In a refrigeration system service environment, there are two concerns regarding the lubricant (oil) separators. First, the service technician should drain the lubricant from the separator following each use of the service system. Otherwise, the purpose of the separator will be defeated when it is over-full. Second, contamination of different refrigerants with different and potentially incompatible lubricants (such as R-12 and PAG lubricant) is a source of concern. In automotive air conditioner service applications, for example, service operators prefer to employ a single unit for servicing both R-12 and R-134a systems. In such units employing a common lubricant separator for both refrigerants, as disclosed for example in U.S. application Ser. No. 08/357,929, potential lubricant contamination is of particular concern. SAE Standard J1770 applicable to combined R-12/R-134a refrigerant service equipment requires an interlock to ensure that lubricant is drained from the separator before clearing the system of one refrigerant and connecting to a system with a different refrigerant.
It is a general object of the present invention to provide a refrigerant handling system and method, particularly a refrigerant recovery system and method for use in a refrigeration system service environment, that facilitate separation and draining of lubricant from refrigerant. A more specific object of the present invention is to provide a system and method of the described character that includes facility for monitoring refrigerant pressure at the lubricant separator, and either manually or automatically draining lubricant from the separator when refrigerant pressure reaches a preselected level. A further object of the present invention is to provide a system and method of the described character having a compressor for pumping refrigerant and a pressure equalization valve connected between the compressor inlet and outlet for equalizing pressure across the compressor during non-operation of the compressor, and in which draining of lubricant at the separator is facilitated by refrigerant pressure during pressure equalization.